This invention relates to gaseous fuel powered internal combustion engines and more particularly it relates to a method of operating an internal combustion engine using natural gas.
Natural gas is considered an excellent source of fuel for an internal combustion engine because it burns cleaner and there exist large reserves of natural gas. However, the use of natural gas to fuel internal combustion engines is not without problems. For example, there is no easy method of refueling vehicles employing natural gas. Further, natural gas requires more fuel tank volume to obtain equivalent miles when compared to diesel or gasoline powered vehicles. In addition, the use of natural gas for fuel for an internal combustion engine can result in exhaust emission problems requiring combinations of exhaust gas recirculation, positive crankcase ventilation, and catalytic converters to care for the various compounds in the exhaust gases. For example, U.S. Pat. Nos. 5,660,602; 5,666,923 and 5,787,864 disclose alternative gaseous fuel for operating a combustion engine including approximately 21 to 50% hydrogen and the rest natural gas constituents such as combinations of methane, carbon dioxide, nitrogen, ethane, propane, iso-butane, n-butane, iso-pentane, n-pentane, and hexanes, as well as others. Current production engines without any substantial modifications can use such alternative fuel which is lean burning and emits emissions that are below current legal standards.
It is also known to reform methanol to produce hydrogen for use with gasoline for internal combustion engines to reduce noxious components. For example, U.S. Pat. Nos. 4,244,328 and 4,340,013 disclose an improved process and apparatus for preparing a gaseous mixture of hydrocarbon and carbon monoxide to be supplied to the air/fuel mixture of a combustion engine. The process and apparatus are useful in reducing the amount of noxious components and aldehydes in the engine exhaust gas. In one embodiment of the invention an improved process and combustion engine are provided for reducing the noxious components and aldehydes.
U.S. Pat. No. 4,147,136 discloses a fuel reforming system for an internal combustion engine which has a fuel reforming reactor to be supplied with a hydrocarbon fuel. The reactor contains a catalyst carrier and a catalyst thereon to be heated for facilitating a conversion of the fuel into a reformed gaseous mixture rich with hydrogen which mixture is to be fed into the engine. The catalyst is periodically alternately exposed to the fuel and air so that carbon produced and deposited on the catalyst during the fuel reforming reaction facilitated by the catalyst is burnt away from the catalyst carrier and the catalyst thereon whereby the catalytic performance of the catalyst is restored to ensure a prolonged operative life thereof. The reformed gaseous mixture assures a reliable ignition and combustion of a mixture thereof with air in the engine at a very lean air-fuel ratio to advantageously decrease the emission of harmful components of engine exhaust gas.
U.S. Pat. No. 4,476,817 discloses a combustion and pollution control system wherein a controlled amount of a fluid (steam or water or a solution of water plus additives) is injected into an internal combustion engine to improve combustion, efficiency, and to reduce emissions. The amount of the fluid injected is controlled in response to engine need. The steam is generated by the heat produced by the engine. Combustion gas temperature is used to control the amount of steam produced by varying the fluid flow through one or more fixed or variable orifice control valves. The stream is injected in a piston engine to cool peak temperatures, to prevent detonation and pre-ignition, to smooth out hot spots, to prevent auto-ignition or dieseling, and to use the vapor energy in the expansion cycle to increase low speed torque and acceleration. The steam is used to cause full retard of the vacuum spark advance during acceleration at full load from low speed, and a large amount of steam is injected at this point in the cycle to prevent pre-ignition and detonation. Ultrasonic energy is added to the injected steam to produce better mixing and distribution. Hydrogen is also injected to permit better combustion with higher amounts of air. The hydrogen is produced by the interaction of a catalyst on the steam and fuel hydrocarbons and ultrasonic energy. At times exhaust gas and other additives, such as hydrogen peroxide, methyl alcohol and ammonia are injected.
U.S. Pat. No. 4,318,369 discloses a recyclable-fuel engine system designed for use in a vehicle. The system includes a hydrogen-producing catalytic unit having plural catalytic beds, and a hydrogen-fueled engine having combustion and exhaust chambers. The catalytic beds, when supplied with heat, catalyze a reduced form of a hydrocarbon carrier to hydrogen and a dehydrogenated form of the carrier. One of the catalytic beds is supplied heat by direct heat transfer from the engine""s exhaust chamber. The remaining catalytic beds are supplied heat by heat pipes receiving heat from the combustion and exhaust chambers. The hydrogen produced in the catalytic unit is supplied to the engine, to power the same. Also disclosed are apparatus and method for regenerating the catalytic beds periodically.
U.S. Pat. No. 4,425,876 discloses a method of fuel treatment and distribution for an internal combustion engine including the steps of operating an adiabatic reactor without a substantial amount of exhaust heat within an operational temperature range, the catalyst bed reactor including a partial combustion catalyst and a dissociation catalyst. A substantial amount of engine exhaust heat is provided to an endothermic reactor having an endothermic dissociation catalyst therein and liquid alcohol is vaporized to form alcohol vapor. The alcohol vapor is mixed with air to form a partial combustion mixture which is contacted with the partial combustion catalyst whereby a dissociation mixture is formed and heat is evolved. The dissociation mixture and the dissociation catalyst form a hydrogen-rich fuel. The hydrogen-rich fuel and the endothermic dissociation catalyst form a fuel product whereby at least a portion of any residual undissociated alcohol in the hydrogen-rich fuel is dissociated to hydrogen and carbon monoxide using the engine waste heat provided by the exhaust gas.
U.S. Pat. No. 4,444,158 discloses a method of methyl alcohol treatment for an automobile internal combustion engine wherein the methyl alcohol is converted to a hydrogen-rich fuel for burning in the internal combustion engine.
U.S. Pat. No. 4,475,484 discloses an apparatus for the catalytic transformation of fuel for use with an internal combustion engine. The apparatus comprises a catalytic reactor in the form of a chamber containing catalytic material, and through which liquid or vaporized fuel is passed, the reactor chamber being in close thermal communication with the exhaust gases leaving the internal combustion engine. Said reactor chamber is either placed within the exhaust gas chamber of the engine exhaust manifold, or in very close proximity thereto. In a preferred arrangement, there are two reactor chambers in series, one being formed within the exhaust manifold of the engine, and the other being mounted closely adjacent thereto.
U.S. Pat. No. 4,547,356 discloses a method for generating hydrogen. The system includes a reactor that has reaction zones wherein catalyst and elevated temperatures generate hydrogen from steam. The zones in the reactor are in the form of tubes about a heat generating chamber, and the zones are adapted to be interconnected to each other, to atmosphere, and to the source of steam, all to maximize the generation of hydrogen by providing a reactor of optimum flexibility.
U.S. Pat. No. 5,156,114 discloses an aqueous fuel for an internal combustion engine. The fuel comprises water from about 20 percent to about 80 percent by volume of the total volume of said fuel, and a carbonaceous fuel selected from the class consisting of ethanol, methanol, gasoline, kerosene fuel, diesel fuel, carbon-containing gaseous or liquid fuel, diesel fuel, carbon-containing gaseous or liquid fuel, or mixtures thereof. A method for combusting an aqueous fuel in an internal combustion engine is provided. The method produces approximately as much power as the same volume of gasoline. The method comprises introducing air and aqueous fuel into a fuel introduction system for the engine. The fuel comprises water from about 20 percent to about 80 percent by volume of the total volume of the fuel, and a carbonaceous fuel from ethanol, methanol, gasoline, kerosene fuel, diesel fuel, carbon-containing gaseous or liquid fuel, or mixtures thereof, and introducing and combusting said air/fuel mixture in a combustion chamber or chambers in the presence of a hydrogen producing catalyst to operate the engine.
U.S. Pat. No. 5,297,515 discloses an engine which, in at least one cylinder or combustion area, is provided with a hydrocarbon rich fuel which produces upon combustion an exhaust gas containing unburned hydrocarbons, water vapor and carbon monoxide. The exhaust gas is treated in a catalytic converter and the reaction process that occurs therein produces hydrogen and carbon dioxide which is mixed with air to form a hydrocarbon lean, hydrogen enriched mixture. The mixture is subsequently ignited in other cylinders or combustion areas of the engine to produce power.
U.S. Pat. No. 5,488,932 discloses a gaseous fuel-enriching subsystem for an internal combustion engine including a supplemental intake conduit to an intake manifold internal combustion engine. Such supplemental input is provided with numerous apertures therein. An exhaust gas conduit from the internal combustion engine annularly surrounds the intake conduit permitting fuel values from exhaust in the exhaust conduit to enter the supplemental intake conduit through such apertures. A water supply input to the supplemental intake conduit, at an end opposite to the location of the manifold, provides a further fuel input to the supplemental intake conduit in that water from the water supply is evaporated and then hydrolyzed, separating the water into its chemical constituents of hydrogen and oxygen, thusly producing an enriched gaseous fuel mixture with the recycled exhaust gas which is fed to the manifold.
In spite of these disclosures, there is still required a method of operating an internal combustion engine on a gaseous fuel such as natural gas or propane which permits significant charge dilution without engine misfire to produce exhaust gas with near-zero NOx.
It is an object of this invention to provide a method of operating an internal combustion engine.
It is a further object of this invention to provide an improved method of operating a combustion engine to provide an exhaust gas having near-zero NOx using charge dilution by recycling exhaust gas.
It is still another object of the invention to provide an improved method for operating a combustion engine on gaseous fuel such as natural gas or propane or the like to provide an exhaust gas having near-zero NOx using charge dilution.
Yet it is another object of the invention to provide an improved method for operating an internal combustion engine on a gaseous fuel comprised of natural gas and hydrogen and carbon monoxide using exhaust gas recycle to produce low NOx and lean burn conditions to obtain low carbon monoxide.
These and other objects will become apparent from a reading of the specification and claims appended hereto.
In accordance with these objects, there is provided a method of producing near-zero NOx and near-zero CO emissions in exhaust gas from an internal combustion engine using a gaseous fuel. The method comprises providing an internal combustion engine having intakes for fuel and air and an having exhaust gas. A first portion of the exhaust gas is recycled for adding to the engine air intake. A second portion of the exhaust gas is discharged to the atmosphere. A gaseous fuel comprised of natural gas and at least one additional gas selected from hydrogen and carbon monoxide is provided for adding to the engine. The engine is operated to combust the fuel and the first portion of exhaust gas with air under exhaust gas recycle conditions which produce near-zero NOx emissions in said exhaust gas emitted from said engine and under lean burn conditions which provide up to 4% oxygen in the exhaust gas emitted from the engine. Carbon monoxide in the second portion of the exhaust gas is oxidized using said oxygen and an oxidizing gas catalyst. Thus, exhaust gas discharged to the atmosphere has both near-zero carbon monoxide emission and near-zero NOx.